1. Field of the Invention
The present invention relates to a process for preparing carbonyl compounds and, more particularly, to a process for efficiently and stably preparing carbonyl compounds including ketones, particularly such as methyl ethyl ketone, methyl isobutyl ketone, acetone, cyclopentanone, etc., and aldehydes, such as acetaldehyde, etc., by oxidizing olefins. The carbonyl compounds are useful as solvents, raw chemical materials and so on.
2. Description of the Released Art
Carbonyl compounds including ketones such as methyl ethyl ketone, methyl isobutyl ketone, acetone, etc. and aldehydes such as acetaldehyde, etc. are useful as solvents and raw chemical materials and so on.
As the method for the preparation of the carbonyl compounds by the direct oxidation of olefins, there is known the Wacker type oxidation process in which PdCl.sub.2 --CuCl.sub.2 is employed as a catalyst. The Wacker type process requires a relatively large quantity of an active chlorinated compound so that it causes the problems with corrosion of equipment, by-production of chlorinated compounds, and so on. Further, the Wacker type oxidation has the defects that a reaction rate is decreased to a remarkable extent as the number of carbons of raw olefin materials increases, and that the reactivity of the internal olefins is low, so that the Wacker type process is industrially applicable only to the production of lower carbonyl compounds such as acetoaldehyde, acetone and so on.
In order to solve those problems, various process have recently been proposed in which catalysts of a new type are employed, in place of a so-called Wacker type catalyst. Those processes, however, are said to be industrially insufficient.
For example, Japanese Patent Laid-Open Publication (kokai) No. 51-117,189 discloses a process in which there is employed a catalyst composed of a combination of a Pd compound with a heteropolyacid or with an isopolyacid.
As the conventional process employs water as a solvent, however, it suffers from the disadvatnages that the reaction rate becomes low, productivity becomes poor, and so on. The reason for the low reaction rate is because of the raw olefin material employed is less soluble in a solution containing catalyst (an aqueous solution) and the efficiency in the contact of the raw olefin material with the solution containing catalyst (or a catalyst component) becomes remarkably poor. In addition, this conventional process employs a largely excessive quantity of the heteropolyacid or isopolyacid, relative to the palladium compound, so that a large quantity of the heteropolyacid or the isopolyacid is required in order to ensure the sufficiently high reaction rate. This is disadvantageous in terms of economy and this is further a cause of various problems as will be described hereinafter.
It is to be noted that this conventional process can reduce the problem with corrosion of equipment to a considerably low level, as compared with the Wacker type process which requires a large quantity of the active chlorinated compounds, particularly CuCl.sub.2 or hydrochloric acid, however, the problem with corrosion of equipment cannot be said to be solved to a sufficient extent. In fact, this conventional process requires the use of an anti-corrosive agent, such as polyethyl siloxane and so on, and the adjustment of pH of a solution containing catalyst with sulfuric acid to, for example, pH=1. Further, the heteropolyacid and the isopolyacid are remarkably lower than CuCl.sub.2 or hydrochloric acid in terms of the extent to which equipment causes corrosion. However, they are an acidic compound so that this conventional process suffers from the disadvantage that a large quantity of highly concentrated aqueous solution should be employed. This is disadvantageous in terms of complete prevention of corrosion of equipment and further the use of sulfuric acid is disadvantageous in terms of prevention of corrosion of equipment.
In addition, the conventional process is likely to cause isomerization of olefins. When the raw material to be employed is an olefin having a long chain, the problems are that the reactivity becomes low and the selectively to the objective carbonyl compounds becomes low. For instance, when 1-hexene is employed as the raw material, the isomerization to 2-hexene is promoted and, as a result, the reactivity is so lowered that the conversion and the selectivity to 2-hexanone are caused to be lowered, thereby increasing the by-production of 3-hexanone. The cause that the isomerization is likely to occur is considered to result from the fact that only water is employed as the solvent and that a large quantity of the heteropolyacid or the isopolyacid is employed.
Further, U.S. Pat. No. 4,550,212 discloses a process in which the reaction is carried out in a two-phase solvent composed of decane and water by using a multi-component catalyst, such as a catalyst capable of transferring between phases, obtainable by adding H.sub.3 BO.sub.3 or cetyltrimethylammoniumbromide (a surfactant) to a Pd-heteropolyacid system.
This process takes advantage of the technology of reaction using a catalyst of such a type as transferring between phases in order to improve the efficiency in the contact of the raw olefin material, concentrated by dissolving it mainly in the decane phase, with the catalyst component that exists mainly on the side of the aqueous solution via the action of the surfactant.
It is to be noted, however, that this conventional process basically employs a two-phase type solvent composed of decane and water, which are not incompatible with each other. Hence, this conventional process presents the problems that the efficiency in the contact between the raw olefin material and the catalyst is insufficient and the reaction rate is slow. Further, this process has the defect that the reactivity of 2-butene is lower than that of 1-butene. In addition, this conventional process is of a multi-component system in which the reaction system is complex, so that it presents the drawbacks that the separation and recovery of the product, solvent, catalyst components and so on are laborious.
In addition, Patent Laid-open Publication (kohyo) No. 63-500,923 proposes a process using a catalyst system in which a redox metal, such as Cu, Fe, Mn or the like, and/or ligand (acetonitrile or the like) are added to a Pd-polyoxoanion system.
In this case, however, the addition of either of the redox metal or the ligand provides merely the small effect of improvements in the catalyst activity and the improvements in the catalyst activity depends largely upon the synergy between the redox metal and the ligand. Hence, the problems are that the catalyst system becomes complex as a matter of course as well as the separation and recovery of the catalyst components and so on are as laborious as the other conventional process as described hereinabove. Further, this conventional process presents the severe problem that the sedimentation of the catalyst component is caused to occur as the reaction proceeds, thereby lowering the reaction rate to a remarkably low level, although the reactivity in the initial stage of the reaction is relatively good.
Further, Japanese Patent Laid-Open Publication (kokai) No. 62-223,145 proposes a process in which the reaction is carried out in a solvent containing a carbamoyl group in the presence of a catalyst system obtainable by adding water to a Pd-redox metal salt-quinone catalyst.
This process, however, presents the problems that the reactivity is low and, if the raw olefin material is an internal olefin, the reactivity becomes lower than when the raw olefin material is a terminal olefin.
In addition, Jan-E. Backvall et al., J. Am. Chem. Soc., vol. 112, pages 5,160-5,166 (1990) proposes a process using a catalyst composed of a Pd-polycyclic metal-quinone-perchloric acid system. Fe-porphyrin is the most useful as the polycyclic metal to be employed in this process.
This conventional process employed, however, is extremely small in scale, although the reaction rate is improved, as compared with the usual Wacker type process. Further, this process causes the isomerization to occur from the terminal olefin to the internal olefin due to the presence of a perchloric acid and these the internal olefin are less inreactivity. In addition, this process presents the drawback that the Pd settles rapidly in the absence of the acid. Moreover, porphyrin compounds, using in this reaction system, are known to be unstable in general.
As described hereinabove, those conventional processes, however, have the drawbacks as described hereinabove, so that they are not yet practically applicable on an industrial scale. Demands have been strongly made to develop improvements in technology that can solve those problems and realize industrialization with ease.
The present invention has been performed on the basis of the situation as described hereinabove.